Tag: senescent cells

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High-fat Diets are ‘Ticking Time Bombs’ for Liver Cancer

On By ModernMedia
These images show slices of mouse liver under the microscope, with tumours outlined in yellow and green indicating the expression of different proteins within cells. The left column is a control group. In the centre column, the protein detected (TBG-Cre) is expressed in all liver cells, so the entire image appears green. In the right column, the protein detected (p21-Cre) is only expressed in senescent liver cells. Because green is only visible within the tumour area, the results show that liver tumours originate from previously senescent liver cells. Photo credit: UC San Diego Health Sciences

A new study on the development of liver cancer reveals a complex interplay between cellular metabolism and DNA damage that drives the progression of fatty liver disease to cancer. The findings, published in Nature, suggest new paths forward for preventing and treating liver cancer and have significant implications on our understanding of cancer’s origin and the effects of diet on our DNA.

The incidence of the most common form of liver cancer, hepatocellular carcinoma (HCC), has grown by 25-30% in the past two decades, with much of the growth attributed to the dramatic rise in fatty liver disease. About 20% of individuals with fatty liver disease have a severe form of the disease, called metabolic dysfunction-associated steatohepatitis (MASH), that greatly increases the risk of HCC. However, how MASH transitions to liver cancer is not well understood.

“Going from fatty liver disease to MASH to liver cancer is a very common scenario, and the consequences can be deadly,” said Michael Karin, PhD, Distinguished Professor in the Department of Pharmacology at UC San Diego School of Medicine. MASH ends up destroying the liver, or leading to often-fatal liver cancer, but little is know of the process at the subcellular level.

The researchers used a combination of mouse models and human tissue specimens and databases to demonstrate that MASH-inducing diets, which are rich in fat and sugar, cause DNA damage in liver cells that causes them to go into senescence, a state in which cells are still alive and metabolically active but can no longer divide. Senescence is a normal response to a variety of cellular stressors. In a perfect world, senescence gives the body time to repair damage or eliminate the damaged cells before they’re allowed to proliferate more widely and become cancerous.

“A poor, fast-food diet can be as dangerous as cigarette smoking in the long run. People need to understand that bad diets do far more than just alter a person’s cosmetic appearance. They can fundamentally change how our cells function, right down to their DNA.”

Michael Karin, PhD

However, as the researchers discovered, this isn’t what happens in liver cells, also known as hepatocytes. In hepatocytes, some damaged cells survive this process.

These cells are, according to Karin, “like ticking time bombs that could start proliferating again at any point and ultimately become cancerous.”

“Comprehensive genomic analyses of tumour DNA indicate that they originate from liver cells damaged by MASH, emphasising a direct link between diet-induced DNA damage and the development of cancer,” added study co-author Ludmil Alexandrov, PhD, associate professor of cellular and molecular medicine and bioengineering at UC San Diego and member of UC San Diego Moores Cancer Center.

The findings suggest that developing new drugs to prevent or reverse DNA damage could be a promising therapeutic approach for preventing liver cancer, particularly in people with MASH.

“There are a few possibilities for how this could be leveraged into a future treatment, but it will take more time and research to explore these ideas,” said Karin. “One hypothesis is that a high-fat diet could lead to an imbalance in the raw materials our cells use to build and repair DNA, and that we could use drugs or nutri-chemicals to correct these imbalances. Another idea is developing new antioxidants, much more efficient and specific than the ones we have now, and using those could help block or reverse the cellular stress that causes DNA damage in the first place.”

In addition to opening these new avenues of treatment for liver cancer, the study also offers new insight into the relationship between aging and cancer.

“We know that aging increases the risk of virtually all cancers and that aging is associated with cellular senescence, but this introduces a paradox since senescence is supposed to guard against cancer,” said Karin. “This study helps reveal the underlying molecular biology that allows cells to re-enter the cell cycle after undergoing senescence, and we believe that similar mechanisms could be acting in a wide range of cancers.”

The findings also help directly quantify the detrimental effects of poor diet on cellular metabolism which, according to Karin, could be used to help guide public health messaging related to fatty liver disease.

“A poor, fast-food diet can be as dangerous as cigarette smoking in the long run,” said Karin. “People need to understand that bad diets do far more than just alter a person’s cosmetic appearance. They can fundamentally change how our cells function, right down to their DNA.”

Source: University of California – San Diego

Categories : AgeingTags :

Ground-breaking Identification of Key Enzyme in Aging Cells

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Photo by National Cancer Institute on Unsplash

A team at Kumamoto University has made a ground-breaking discovery in the field of aging and inflammation. The research focuses on “cellular senescence,” a process where cells stop dividing and enter a state associated with chronic inflammation and aging. This cellular state, known as the senescence-associated secretory phenotype (SASP), involves the secretion of inflammatory proteins that accelerate aging and disease, such as dementia, diabetes, and atherosclerosis.

The researchers found that ATP-citrate lyase (ACLY), an enzyme involved in converting citrate to acetyl-CoA, plays a critical role in activating SASP. This discovery was made using advanced sequencing and bioinformatics analyses on human fibroblasts, a type of cell found throughout the body. They demonstrated that blocking ACLY activity, either genetically or with inhibitors, significantly reduced the expression of inflammation-related genes in aging cells. This suggests that ACLY is a crucial factor in maintaining the pro-inflammatory environment in aged tissues.

Furthermore, the study revealed that ACLY-derived acetyl-CoA modifies histones, proteins that DNA wraps around, allowing the chromatin reader BRD4 to activate inflammatory genes. By targeting the ACLY-BRD4 pathway, the researchers were able to suppress inflammation responses in aged mice, highlighting the potential of ACLY inhibitors in controlling chronic inflammation while maintaining healthy aging.

This discovery opens new avenues for developing treatments that specifically target the harmful aspects of aging cells without removing them, offering a promising strategy for managing aging and age-related diseases. The research provides a stepping stone toward therapies that can control cellular aging, promoting longer, healthier lives.

Categories : AgeingTags :

Friendly ‘Zombie’ Cells Help Promote Tissue Repair

On By ModernMedia
Photo by julien Tromeur on Unsplash

While most senescent cells may be harmful “zombies” spewing toxic compounds and should be targeted to reduce the risk of age-related disease, not all of them are like this. In fact, according to new research in Science, some of them embedded in young, healthy tissues seem to help repair damage.

Scientists have now seen these cells in action in lung tissue, as well as other organs that serve as barriers in the body, such as the small intestine, colon and skin. When they used drugs called senolytics to kill these cells, injuries to lung tissues healed more slowly.

“Senescent cells can occupy niches with privileged positions as ‘sentinels’ that monitor tissue for injury and respond by stimulating nearby stem cells to grow and initiate repair,” said Tien Peng, MD, associate professor of pulmonary, critical care, allergy and sleep medicine, and senior author of the study.

Ageing cells can both damage and heal

A/Prof Peng said it was understandable that scientists at first viewed senescent cells as purely detrimental. As people age, senescent cells – often termed “zombie cells” – accumulate that have characteristics of old, worn-out cells, including the inability to make new cells. Instead of dying like normal aged cells, they to live on, spewing a cocktail of inflammatory compounds that form the senescence associated secretory phenotype (SASP). These factors are linked to Alzheimer’s disease, arthritis, and other age-related maladies including cancer.

Using senolytics that selectively kill “zombie cells,” researchers made the exciting discovery that clearing senescent cells from animals thwarted or diminished age-related disease and extended the lifespan of the animals. Thereafter, a boom of activity ensued in research labs and pharmaceutical companies focused on discovering and refining more powerful versions of these drugs.

But killing off senescent cells has dangers, A/Prof Peng said. For one thing, this current study showed that senescent cells also possess the ability to promote normal healing through activation of stem cell repair. “Our study suggests that senolytics could adversely affect normal repair, but they also have the potential to target diseases where senescent cells drive pathologic stem cell behaviour,” said A/Prof Peng.

Lighting up senescent cells

One major challenge to studying senescent cells is that biomarkers of senescence (such as the gene p16) are often quite sparse, making it difficult to detect the cells. In early experiments, researchers extracted cells called fibroblasts into culture dishes, allowing them to grow and produce enough cells to experiment with, and then stressed the cells with chemicals that induced them to become senescent. But in living organisms, cells interact with tissues around them, strongly affecting the cells’ gene activity. This means that the characteristics of cells growing isolated in a glass dish could be quite different from that of cells in their natural environment.

To create a more powerful tool for their studies, the researchers improved on a common technique of fusing a relevant gene – in this case, the p16 gene, which is overly active in senescent cells –with green fluorescent protein (GFP) as a marker that can reveal the location of the cells under ultraviolet light. By enhancing the quantity and stability of green fluorescent protein in these senescent cells, the fluorescent signal was greatly amplified, finally enabling the researchers to see senescent cells in their natural habitat of living tissues.

“Zombies” stimulate stem cells shortly after birth

Using this highly sensitive tool, the researchers found that senescent cells exist in young and healthy tissues to a greater extent than previously thought, and actually begin appearing shortly after birth. The scientists also identified specific growth factors that senescent cells secrete to stimulate stem cells to grow and repair tissues. Relevant to aging and tissue injury is the discovery that cells of the immune system such as macrophages and monocytes can activate senescent cells, suggesting that inflammation seen in aged or damaged tissue is a critical modifier of senescent cell activity and regeneration.

In their studies of lung tissue, A/Prof Peng’s team observed green glowing senescent cells lying next to stem cells on the basement membrane that serves as a barrier preventing foreign cells and harmful chemicals from entering the body and also allows oxygen to diffuse from air in the lungs into underlying tissues. Damage can occur at this dynamic interface. The team saw senescent cells in similar positions in other barrier organs such as small intestine, colon, and skin, and their experiments confirmed that if senescent cells were killed with senolytics, lung stem cells were not able to properly repair the barrier surface.

Source: EurekAlert!